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PORelayCommand.CanExecute not updating IsEnabled in UI
 

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  1. PORelayCommand.CanExecute not updating IsEnabled in UI
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    <p>I have a Windows Phone 8 app and I have a <code>RelayCommand</code> Instance called <code>DiscoverExpansionModulesCommand</code>. I have a button with the <code>Command</code> property bound to <code>DiscoverExpansionModulesCommand</code>. When the app first loads, the button is enabled or disabled properly. However, when on the page and I want to change whether the command can execute, the method <code>CanExecuteDiscoverExpansionModulesCommand()</code> properly fires and it returns the proper true or false value, but the button does not reflect it. Why isn't button updating it's UI? I found another article on this issue here <a href="http://social.msdn.microsoft.com/Forums/en-US/silverlightarchieve/thread/48a341e4-f512-4c33-befd-b614404b4920/" rel="nofollow">http://social.msdn.microsoft.com/Forums/en-US/silverlightarchieve/thread/48a341e4-f512-4c33-befd-b614404b4920/</a></p> <p>My ViewModel:</p> <pre><code>using GalaSoft.MvvmLight; using GalaSoft.MvvmLight.Command; using GalaSoft.MvvmLight.Messaging; using MAL.Portable.Commands; using MAL.Portable.Message; using MAL.Portable.Model; using System; using System.Collections.Generic; using System.Windows.Input; namespace MAL.Portable.ViewModel { public class SettingsViewModel : ViewModelBase { // Define an observable collection property that controls can bind to. private List&lt;Setting&gt; settings; private String controllerUrl; private String controllerPort; private String temperature; private Wifi wifi; private Boolean connected; private Boolean checkingConnection; public SettingsViewModel() { DiscoverExpansionModulesCommand = new RelayCommand(OnDiscoverExpansionModules, CanExecuteDiscoverExpansionModulesCommand); Messenger.Default.Register&lt;RetrieveSettingsMessage&gt; ( this, (action) =&gt; RetrievedListsMessage(action) ); Messenger.Default.Send&lt;GetSettingsMessage&gt;(new GetSettingsMessage()); } public ICommand DiscoverExpansionModulesCommand { get; private set; } public String ConnectionStatus { get { if (checkingConnection) return "checking"; else return connected ? "connected" : "not connnected"; } } private Boolean CanExecuteDiscoverExpansionModulesCommand() { return connected; } private void OnDiscoverExpansionModules() { } private void CheckConnection() { wifi = null; if (!String.IsNullOrWhiteSpace(ControllerUrl) &amp;&amp; !String.IsNullOrWhiteSpace(ControllerPort) &amp;&amp; !checkingConnection) { checkingConnection = true; wifi = new ReefAngelWifi(controllerUrl, controllerPort); wifi.TestConnectionComplete += wifi_TestConnectionComplete; wifi.RequestFail += wifi_RequestFail; wifi.BeginTestConnection(); } } private void wifi_RequestFail(object sender, RequestExceptionEventArgs e) { connected = false; checkingConnection = false; RaisePropertyChanged("ConnectionStatus"); } private void wifi_TestConnectionComplete(object sender, TestConnectionEventArgs e) { connected = e.TestSuccessful; checkingConnection = false; DiscoverExpansionModulesCommand.CanExecute(null); RaisePropertyChanged("ConnectionStatus"); RaisePropertyChanged("DiscoverExpansionModulesCommand"); } private object RetrievedListsMessage(RetrieveSettingsMessage action) { settings = action.Settings; CheckConnection(); return null; } private String GetStringValue(String key) { if (settings == null) return String.Empty; var item = settings.Find(x =&gt; x.Key == key); if (item == null) return String.Empty; else return item.Value; } private Boolean GetBooleanValue(String key) { if (settings == null) return false; var item = settings.Find(x =&gt; x.Key == key); if (item == null) return false; else return Boolean.Parse(item.Value); } } } </code></pre> <p>And the XAML</p> <pre><code>&lt;phone:PhoneApplicationPage xmlns:ReefAngel="clr-namespace:MAL.WindowsPhone8" xmlns:Controls="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Input" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone" xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity" xmlns:cmd="clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Platform.WP8" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:telerikPrimitives="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Primitives" x:Class="MAL.WindowsPhone8.ReefAngel.SettingsPage" xmlns:converter="clr-namespace:MAL.WindowsPhone8.Converters" FontFamily="{StaticResource PhoneFontFamilyNormal}" FontSize="{StaticResource PhoneFontSizeNormal}" DataContext="{Binding Settings, Source={StaticResource Locator}}" SupportedOrientations="Portrait" Orientation="Portrait" mc:Ignorable="d" shell:SystemTray.IsVisible="True"&gt; &lt;phone:PhoneApplicationPage.Resources&gt; &lt;converter:BooleanToStringConverter x:Key="temperatureConverter" TrueString="Celsius" FalseString="Fahrenheit" /&gt; &lt;converter:BooleanToStringConverter x:Key="timeFormatConverter" TrueString="24 hour" FalseString="12 hour" /&gt; &lt;converter:BooleanToStringConverter x:Key="dateFormatConverter" TrueString="dd/mm/yyyy" FalseString="mm/dd/yyyy" /&gt; &lt;/phone:PhoneApplicationPage.Resources&gt; &lt;!--LayoutRoot is the root grid where all page content is placed--&gt; &lt;Grid x:Name="LayoutRoot" &gt; &lt;phone:Pivot Title="{Binding LocalizedResources.ApplicationTitle, Source={StaticResource LocalizedStrings}, StringFormat='\{0\} Settings'}"&gt; &lt;phone:PivotItem Header="connection"&gt; &lt;Grid&gt; &lt;StackPanel Margin="12,0,0,0"&gt; &lt;TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="Reef Angel Wifi Address"/&gt; &lt;TextBox Height="72" TextWrapping="Wrap" Text="{Binding ControllerUrl, Mode=TwoWay}"/&gt; &lt;TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="Reef Angel Wifi Port"/&gt; &lt;TextBox Height="72" TextWrapping="Wrap" Text="{Binding ControllerPort, Mode=TwoWay}"/&gt; &lt;StackPanel Orientation="Horizontal"&gt; &lt;TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="Reef Angel Wifi Status : "/&gt; &lt;TextBlock Margin="0,20,0,0" TextWrapping="Wrap" Text="{Binding ConnectionStatus, Mode=OneWay}"/&gt; &lt;/StackPanel&gt; &lt;/StackPanel&gt; &lt;/Grid&gt; &lt;/phone:PivotItem&gt; &lt;phone:PivotItem Header="expansion"&gt; &lt;Grid&gt; &lt;Button Content="Discover Expansion Modules" x:Name="DiscoverButton" Command="{Binding DiscoverExpansionModulesCommand, Mode=OneWay}" /&gt; &lt;/Grid&gt; &lt;/phone:PivotItem&gt; &lt;/phone:Pivot&gt; &lt;/Grid&gt; &lt;/phone:PhoneApplicationPage&gt; </code></pre> <p>I am using the MVVM Light Portable Class Libraries.</p>
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    1. USKeenan Newton
    1. USKeenan Newton
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    1. COCan you please show the view model and xaml you're using that demonstrates the problem? Without this information we'd just be guessing.
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      1. PORelayCommand.CanExecute not updating IsEnabled in UI
      1. USMatt Lacey
 

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